Along with recent adoption of IP/Ethernet® technology in user traffic, packetization of a carrier network is underway in order to efficiently accommodate packet traffic. A SONET/SDH-based network has used a carrier-class fine monitoring/control (OAM: Operations, Administration and Maintenance) function to respond to a carrier-grade service request. The SONET/SDH is a general term for SONET (Synchronous Optical NETwork) and SDH (Synchronous Digital Hierarchy). Hereinafter, “network” is often referred to as “NW”.
Under a circumstance where a SONET/SDH carrier NW is shifted to a packet NW, the packet NW is required to realize an equivalent level of the OAM function to that of the carrier NW, and vigorous discussion is underway toward standardization.
For example, the OAM for Ethernet® is recommended in ITU-T (International Telecommunication Union Telecommunication Standardization Sector) Y. 1731. Further, also for a MPLS-TP currently attracting attention as a MPLS-based packet transport technology, the OAM function is on the way to standardization as one of striking functions in IETF.
The OAM function is classified into a Fault Management function that performs detection, notification, and localization of a fault and a Performance Monitor function (hereinafter, referred to as “PM function”) that monitors performance of data traffic.
The PM function typically includes a Delay Measurement function (hereinafter, referred to as “DM function”), a Loss Measurement function (hereinafter, referred to as “LM function”).
The above DM function includes a 1-way DM function that measures a one-way delay time between a transmission source node to a transmission destination node and a 2-way DM function that measures a round-trip delay time between the transmission source node to transmission destination node.
In the 1-way DM function, the transmission source node stores a transmission time in a delay measurement OAM packet (hereinafter, referred to as “DM packet”) on the assumption that the source and transmission destination nodes are time-synchronized with each other. Then, the transmission destination node calculates a delay time from a difference between a reception time and the transmission time stored in the DM packet. As a related art, a technique disclosed in PTL 1 can be cited. In the technique disclosed in PTL 1, a quality measurement device 3A transmits a measurement packet intermittently at regular intervals, and a quality measurement device 3B receives the measurement packet. Thereafter, a management device 2 calculates communication quality of the measurement packet based on a transmission/reception state with respect to the measurement packet transmitted/received by both the quality measurement devices 3A and 3B.
In the 2-way DM function, a delay time is calculated from a difference between a transmission time of the DM packet (Request) in the transmission source node and a reception time of the DM packet (Reply) sent back from the transmission destination node.
As described above, the time synchronization between the both nodes is not required in the 2-way DM function, whereas the 1-way DM function assumes that the both nodes are time-synchronized with each other. For example, also in the technique disclosed in PTL 1, the time synchronization is required at least between the quality measurement devices 3A and 3B since the measurement delay time is measured from the transmission/reception time of the measurement packet.
However, in a packet network, there may be a case where the time synchronization is difficult to achieve between the nodes. Therefore, the 1-way DM function is required to be able to measure the delay time even in the absence of the time synchronization.
As a method that uses a normal function to measure a 1-way delay even in the absence of time synchronization, there is known a method that utilizes an extended function of IEEE 1588 time synchronization technology.
In IEEE 1588, a Transparent Clock function (hereinafter, referred to as “TC function”) is defined as an extended function of version 2 (hereinafter, IEEE 1588 utilizing the TC function is referred to as “IEEE 1588 v2 w/TC”).
In IEEE 1588 v2 w/TC, each relay node has the TC function that measures a sojourn time of a control packet (packet of IEEE 1588 message) in a node and writes the measured sojourn time in a predetermined field of the control packet for cumulative addition of the sojourn time. With this TC function, in IEEE 1588 v2 w/TC, the sojourn time in the relay node is added to the message every time the control packet passes through the relay node. This allows the transmission destination node to accurately grasp a sum of queuing delays generated in the respective relay nodes when the control packet is forwarded from the transmission source node. The delay includes a fixed delay (propagation delay) and a variable delay such as the above-mentioned queuing delay. The fixed delay that has once been measured between nodes is not changed unless there is a route change. Thus, in the following description, the variable delay for each packet is measured. Note that the fixed delay can be calculated in a management system based on a physical connection state of the nodes and a path setting state or calculated by measuring a round-trip delay for a priority class with forward and backward routes set as a single physical route and by halving the measured value.